1. Field of the Invention
The present invention relates generally autonomous soaring for uninhabited air vehicles (UAVs), particularly to improved endurance for autonomous soaring UAVs, and more particularly to using thermals or convective thermals to improve the performance of UAVs.
2. Description of the Related Art
Glider pilots have been using buoyant plumes of air found in the lower atmosphere, normally referred to as thermals, in order to extend the distance that a glider may travel for many years.
Several systems have been developed to assist pilots of gliders or low-powered aircraft to locate such thermals in order to provide improved range, endurance, or cross-country speed. For example, U.S. Pat. No. 6,012,675 describes a system that monitors air humidity to locate “moist” thermals and U.S. patent application 2004/0129071 describes a system that employs a database of places on the ground that are likely to generate thermals in conjunction with current weather projections to attempt to estimate positions of thermals for pilots.
Over the past several years, it has also been suggested that UAVs could benefit from using thermals in the same manner as piloted aircraft to improve range, endurance, and speed. For instance, Wharington, et al. in “Control of High Endurance Unmanned Air Vehicle” proposes the concept of using thermals to improve the performance of UAVs and discloses a general control scheme that could be applied for the UAV to take advantage of thermals. However, the paper states that a superior control scheme would be necessary for practical application of the concept. Further, Michael J. Allen, the inventor of the present invention, in “Autonomous Soaring for Improved Endurance of a Small Uninhabited Air Vehicle” provides mathematical evidence that UAVs may dramatically improve range and endurance when employing thermals.
However, until the present invention, no known practical control and guidance system has been developed for UAVs to take advantage of the benefits of thermals. Therefore, it is desired to provide a guidance and control system and method for UAVs to locate and use thermals to provide improved range and endurance.